Biochemical studies of acrosome reactions in an in vitro hamster sperm capacitation system will be concerned with: (1) The mechanism of the stimulation of acrosome reactions by serum albumin and or its associated molecules. (2) The identification of endogenous sperm molecules (including enzymes) involved in the acrosome reaction. (3) The interrelationship of exogenous and endogenous molecules in the acrosome reaction.